Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 2 2010 10.5194/bg-7-427-2010 http://www.biogeosciences.net/7/427/2010/ http://www.biogeosciences.net/7/427/2010/bg-7-427-2010.html http://www.biogeosciences.net/7/427/2010/bg-7-427-2010.pdf 427 440 2010-02-02 A case study of eddy covariance flux of N₂O measured within forest ecosystems: quality control and flux error analysis I. Mammarella ivan.mammarella@helsinki.fi P. Werle M. Pihlatie W. Eugster S. Haapanala R. Kiese T. Markkanen Ãœ. Rannik T. Vesala Department of Physics, University of Helsinki, Finland Karlsruhe Institute of Technology KIT, Garmisch-Partenkirchen, Germany ETH Zurich, Switzerland Finnish Meteorological Institute, Helsinki, Finland Eddy covariance (EC) flux measurements of nitrous oxide (N₂O) obtained by using a 3-D sonic anemometer and a tunable diode laser gas analyzer for N₂O were investigated. Two datasets (Sorø, Denmark and Kalevansuo, Finland) from different measurement campaigns including sub-canopy flux measurements of energy and carbon dioxide are discussed with a focus on selected quality control aspects and flux error analysis. Although fast response trace gas analyzers based on spectroscopic techniques are increasingly used in ecosystem research, their suitability for reliable estimates of EC fluxes is still limited, and some assumptions have to be made for filtering and processing data. The N₂O concentration signal was frequently dominated by offset drifts (fringe effect), which can give an artificial extra contribution to the fluxes when the resulting concentration fluctuations are correlated with the fluctuations of the vertical wind velocity. Based on Allan variance analysis of the N₂O signal, we found that a recursive running mean filter with a time constant equal to 50 s was suitable to damp the influence of the periodic drift. 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